This invention relates to a novel method for preparing para-chlorotoluene.
Para-chlorotoluene is a useful organo-synthetic intermediate, and particularly it proves to be an important compound as an intermediate for the production of agricultural chemicals.
For industrial preparation of para-chlorotoluene, there is known a method in which toluene is reacted with chlorine in the presence of a catalyst. Iron chloride is well known as a catalyst for substituting chlorine in the aromatic ring, and toluene is reacted with an equivalent amount of chlorine in the presence of such iron chloride. The composition of the reaction product, as for instance mentioned in Japanese Patent Publication No. 8302/67, usually comprises 13% of unreacted toluene, 48% of ortho-chlorotoluene, 22% of para-chlorotoluene, 3% of meta-chlorotoluene and 14% of poly-chlorotoluenes, and selectivity to para-chlorotoluene is very poor.
Japanese Patent Publication No. 8302/67 shows a method in which toluene is chlorinated by using iron halide and sulfur halide in combination. The ratio of para to ortho is 50:50 at most.
Japanese Patent Publication No. 26775/67 suggests chlorination of toluene by using platinum oxide as catalyst. According to this method, the ratio of para to ortho is approximately 53:47.
Thus, the conventional methods of producing para-chlorotoluene had the disadvantages in that a large amount of ortho-isomer is by-produced and that it was required to use a catalyst such as iron chloride or dangerous chlorine gas. Hence these methods were not always satisfactory for the production of para-chlorotoluene.
This invention intends to give a fundamental solution to these problems of the conventional methods and has for its object to provide a method of mono-chlorinating toluene with extremely high selectivity to para-chlorotoluene.
The attainment of this invention is based on a new and noteworthy finding that when chlorination is carried out through an electrolytic reaction by using a carbonaceous electrode having fixed thereon cyclodextrin (Schardinger dextrin: (C.sub.6 H.sub.10 O.sub.5).sub.6-8) and by making use of the fact that when such fixed cyclodextrin includes toluene therein, there can be accomplished chlorination with high selectivity to para-isomers.